Local etching apparatus and local etching method

ABSTRACT

A local etching apparatus and local etching method improving the throughput of the local etching apparatus by preheating a discharge tube before ignition of the plasma discharge. The local etching apparatus is provided with a plasma generator  1 , an alumina discharge tube  2 , and a heater  6 . The heater  6  is constituted by a heating wire  60 , a power source  61  for supplying voltage to the heating wire  60 , and a voltage regulator  62  for controlling the voltage supplied from the power source  61  to the heating wire  60.  Due to this, it is possible to heat the alumina discharge tube  2  to the desired temperature by the heater  6  immediately before the plasma discharge by the plasma generator  1.  As a result, there is no need to wait with the local etching work until the alumina discharge tube  2  rises in temperature to the desired temperature due to the heat by the plasma discharge, that is, it is possible to perform the local etching work immediately after the plasma discharge.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a local etching apparatus and alocal etching method for locally etching a protrusion on a surface of awafer by radicals or locally etching a relatively thick portion of awafer so as to make the distribution of thickness of the wafer uniform.

[0003] 2. Description of the Related Art

[0004]FIG. 10 is a schematic sectional view of an example of a localetching apparatus of the related art.

[0005] This local etching apparatus is provided with a discharge tube100, a gas feed device 110, a plasma generator 120, and a stage 130.

[0006] Due to this configuration, it is possible to feed gas from thegas feed device 110 to the discharge tube 100, generate microwaves Mfrom a microwave generator 121 of the plasma generator 120 to the insideof a waveguide 122 to cause plasma discharge of the gas in the dischargetube 100, and spray the radicals G produced by the plasma discharge froma nozzle portion 101 of the discharge tube 100 on to a wafer W on thestage 130.

[0007] By making the stage 130 move in the horizontal direction, aportion Wa relatively thicker than a defined thickness on the surface ofthe wafer W (hereinafter referred to as a “relatively thick portion”) isguided directly under the nozzle 101 where the radicals G are sprayedfrom the nozzle 101 to the relatively thick portion Wa to locally etchthe relatively thick portion Wa. By locally etching the entire surfaceof the wafer W in this way, it is possible to make the distribution ofsurface thickness of the wafer W uniform and flatten the surface of thewafer W as a whole.

[0008] The above local etching apparatus of the related art, however,had the following problems.

[0009] The depth of local etching of the wafer W by the radicals Gdepends on the temperature of the discharge tube 100.

[0010]FIG. 11 is a view of the correlation between the surfacetemperature of the discharge tube 100 and the etching depth.

[0011] As shown in FIG. 11, the etching depth by the radicals G becomeslarger along with a rise of the surface temperature of the dischargetube 100. When the surface temperature of the discharge tube 100 reachesa certain value T₀, the etching depth at a temperature above thetemperature T₀ becomes substantially constant.

[0012] At the time of ignition of the plasma discharge in the dischargetube 100, the discharge tube 100 is cold. The temperature of thedischarge tube 100 rises along with time due to the heat of the plasma.Therefore, the etching depth of the wafer W by the radicals G will notstabilize until the surface temperature of the discharge tube 100reaches the above temperature T₀. Accordingly, if the etching work iscommenced before the surface temperature of the discharge tube 100reaches T₀, the etching rate of the wafer W becomes unstable and it isnot possible to flatten the wafer W to a high precision. In view ofthis, in the local etching apparatuses of the related art, it wasnecessary to allow for a long standby time until the surface temperatureof the discharge tube 100 reaches T₀. It was not possible to start theetching work during that period. As a result, the throughput of theflattening of the wafer W was low and the mass producibility was poor.

SUMMARY OF THE INVENTION

[0013] The present invention was made to solve the above problem and hasas its object the provision of a local etching apparatus and localetching method improving the throughput of the local etching apparatusby preheating the discharge tube before ignition of the plasmadischarge.

[0014] To achieve the above object, according to a first aspect of thepresent invention, there is provided a local etching apparatuscomprising: a discharge tube with a spray port of a nozzle portionfacing an object to be etched in a chamber; a plasma generator forcausing plasma discharge of a predetermined gas in the discharge tube soas to produce radicals for locally etching a relatively thick portionpresent on a surface of the object to be etched; and a heater forheating the discharge tube to a predetermined temperature.

[0015] Due to this configuration, it is possible to use the heater toheat the discharge tube to a predetermined temperature, specifically atleast a temperature at which the etching depth of the object to beetched becomes substantially constant. Suitably thereafter, the plasmagenerator is used to cause plasma discharge of a predetermined gas inthe discharge tube to produce radicals for locally etching a relativelythick portion present on the surface of the object to be etched.Further, by making a nozzle portion of the discharge tube move along thesurface of the object to be etched, it is possible to locally etch arelatively thick portion present on the surface of the object to beetched by the radicals sprayed from the nozzle portion. In this way,since it is possible to preheat the discharge tube to at least atemperature at which the etching depth of the object to be etchedbecomes substantially constant, there is no need to wait with the localetching work until the discharge tube rises to that temperature by theheat due to the plasma discharge such as with the local etchingapparatus of the related art and it is possible to immediately performlocal etching at a stable etching depth by performing the local etchingwork.

[0016] Various heaters may be considered for heating the discharge tube,but giving a preferable example of a heater, according to an embodimentof the invention, the heater is provided with: a heating member providedso as to surround the discharge tube and capable of raising thetemperature in accordance with voltage applied thereto; and a voltagecontroller for controlling the voltage applied to the heating member. Inparticular, according to an embodiment of the invention, the heatingmember of the heater is a heating wire wound around the discharge tube.Further, as another preferable example of the heater, according to anembodiment of the invention, the heater is an optical heater which emitsinfrared rays or a laser beam to the discharge tube to heat thedischarge tube. Further, as another example, according to an embodimentof the invention, the heater is provided with: a heating block arrangedso as to surround the discharge tube in a state contacting the outerside of the discharge tube and has a fluid feed port and fluid exhaustport communicating with a fluid storage portion at the inside; and afluid feeder for heating the fluid to a predetermined temperature andfeeding it to the fluid storage portion of the heating block. Inparticular, according to an embodiment of the invention, the heatingblock of the heater is comprised of a thin tube wound around thedischarge tube.

[0017] Note that it is possible to use various types of discharge tubesas the discharge tube for the local etching apparatus. Therefore,according to an embodiment of the invention, the discharge tube used isany one of an alumina discharge tube, an aluminum nitride dischargetube, a sapphire discharge tube, and a quartz discharge tube.

[0018] Note that the steps executed by the local etching apparatuses intheir operation also stand as method inventions.

[0019] Therefore, according to a second aspect of the present invention,there is provided a local etching method comprising: a plasma generatingstep for causing plasma discharge of a predetermined gas in a dischargetube so as to produce radicals and spraying the radicals from a nozzleportion of the discharge tube; a local etching step for locally etchinga relatively thick portion present on the surface of the object to beetched by the radicals sprayed from the nozzle portion while making thenozzle portion of the discharge tube move relatively along the surfaceof the object to be etched; and a heating step for heating the dischargetube at least to a time of start of plasma discharge of the plasmagenerating step to at least a temperature at which the etching depth ofthe object to be etched at the local etching step becomes substantiallyconstant.

[0020] In the heating step, the discharge tube may be heated at leastuntil the time of the start of the plasma discharge of the plasmagenerating step and a heating time is arbitrary.

[0021] Therefore, according to an embodiment of the invention, theheating step is comprised of heating the discharge tube to the abovetemperature at all times. Further, according to an embodiment of theinvention, the heating step is comprised of heating the discharge tubeto the temperature until the start of plasma discharge of the plasmagenerating step.

[0022] The heated location of the discharge tube is arbitrary. As oneexample, according to an embodiment of the invention, the heating stepis comprised of heating a location of the discharge tube between theplasma discharge location and the spray port of the discharge tube tothe temperature.

[0023] Further, according to an embodiment of the invention, the heatingstep is comprised of raising the temperature of a heating membersurrounding the discharge tube by application of voltage so as to heatthe discharge tube to the temperature. Further, according to anembodiment of the invention, the heating step is comprised of emittinginfrared rays or a laser beam to the discharge tube to heat thedischarge tube to the temperature. Further, according to an embodimentof the invention, the heating step is comprised of feeding a heatedfluid into a heating block arranged so as to surround the discharge tubein a state contacting the outer side of the discharge tube so as to heatthe discharge tube to the temperature.

BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The above and other objects, features, and advantages of thepresent invention will become more readily apparent from the followingdetailed description of a presently preferred embodiment of theinvention taken in conjunction with the accompanying drawings, in which:

[0025]FIG. 1 is a partially cutaway schematic view of the configurationof a local etching apparatus according to a first embodiment of thepresent invention;

[0026]FIG. 2 is a partial enlarged sectional view for showing theheater;

[0027]FIG. 3 is a schematic plan view of the state of the nozzle portionscanning a silicon wafer;

[0028]FIG. 4 is a partial enlarged sectional view of a silicon wafer forshowing a local etching process;

[0029]FIG. 5 is a graph of the correspondence between the time whenperforming flattening work without preheating an alumina discharge tubeand the temperature of the alumina discharge tube;

[0030]FIG. 6 is a graph of the correspondence between the time whenperforming flattening work with preheating of an alumina discharge tubeand the temperature of the alumina discharge tube;

[0031]FIG. 7 is a sectional view of the essential portions of a localetching apparatus according to a second embodiment of the presentinvention;

[0032]FIG. 8 is a sectional view of the essential portions of a localetching apparatus according to a third embodiment of the presentinvention;

[0033]FIG. 9 is a sectional view of a modification of a local etchingapparatus;

[0034]FIG. 10 is a schematic sectional view of an example of a localetching apparatus of the related art; and

[0035]FIG. 11 is a view of the correspondence between a surfacetemperature of a discharge tube and an etching rate.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0036] Preferred embodiments of the present invention will be explainednext with reference to the drawings.

[0037] (First Embodiment)

[0038]FIG. 1 is a partially cutaway schematic view of the configurationof a local etching apparatus according to a first embodiment of thepresent invention.

[0039] As shown in FIG. 1, the local etching apparatus is provided witha plasma generator 1, an alumina discharge tube 2, a gas feeder 3, anX-Y drive 4, a Z-drive 5, and a heater 6.

[0040] The plasma generator 1 is a device for causing plasma dischargeof gas inside the alumina discharge tube 2 to produce radicals G and iscomprised of a microwave generator 10 and a waveguide 11.

[0041] The microwave generator 10 is a magnetron and can generate amicrowave M of a predetermined frequency.

[0042] The waveguide 11 is for guiding the microwave M generated by themicrowave generator 10 and is fit over the alumina discharge tube 2.

[0043] At the inside of the left end of the waveguide 11 is attached areflection plate (short plunger) for reflecting the microwave M to forma standing wave. Further, in the middle of the waveguide 11 are attacheda 3-stub tuner 13 for phase alignment of the microwave M and an isolator14 for bending the reflected microwave M heading toward the microwavegenerator 10 90° in direction (surface direction of FIG. 1) to preventthe reflected wave from returning to the generator.

[0044] The alumina discharge tube 2 is a cylinder having a nozzleportion 20 at its lower end and is connected at its upper end to a feedpipe 30 of the gas feeder 3.

[0045] The gas feeder 3 is a device for feeding gas into the aluminadischarge tube 2 and has a SF₆ (sulfur hexafluoride) gas cylinder 31.The gas cylinder 31 is connected to the feed pipe 30 through a valve 32and flow control device 33.

[0046] By adopting this configuration for the plasma generator 1, when agas is fed from the gas feeder 3 to the alumina discharge tube 2 and amicrowave M is generated from the microwave generator 10, plasmadischarge is caused in the alumina discharge tube 2 and activatedspecies gases G produced by the plasma discharge are sprayed from thespray port 21 of the nozzle portion 20.

[0047] An object to be etched, here a silicon wafer W, is designed to beheld by the electrostatic force of a chuck 90 in a chamber 9 when placedon the chuck 90. The chamber 9 is provided with a vacuum pump 91. Thevacuum pump 91 may be used to make the inside of the chamber 9 a vacuum.Further, a hole 92 is formed in the center of the top surface of thechamber 9. The nozzle portion 20 of the alumina discharge tube 2 isinserted through this hole 92 into the chamber 9. An O-ring 93 isattached between the hole 92 and the alumina discharge tube 2 so as tohold the space between the hole 92 and the alumina discharge tube 2air-tight.

[0048] A duct 94 is provided around the nozzle portion 20 inserted intothe hole 92. By driving the vacuum pump 95, the reaction product gas atthe time of etching is exhausted to the outside of the chamber 9.

[0049] The X-Y drive 4 is arranged inside the chamber 9 and supports thechuck 90 from below.

[0050] The X-Y drive 4 makes the chuck 90 move in the lateral directionin FIG. 1 by an X-drive motor 40 and makes the chuck 90 and the X-drivemotor 40 move together in the direction perpendicular to the surface ofthe paper on which FIG. 1 is drawn by a Y-drive motor 41. That is, it ispossible to make the nozzle portion 20 move in the X-Y directionrelative to the silicon wafer W by the X-Y drive 4.

[0051] A Z-drive 5 supports the X-Y drive 4 in the chamber 9 from below.The Z-drive 5 makes the X-Y drive 4 move in the vertical direction by aZ-drive motor 50 and enables the distance between the spray port 21 ofthe nozzle portion 20 facing the silicon wafer W side and the surface ofthe silicon wafer W to be adjusted.

[0052] The drive operations of the X-drive motor 40 and Y-drive motor 41of the X-Y drive 4 and the Z-drive motor 50 of the Z-drive 5 arecontrolled by a control computer 45 based on a predetermined program.

[0053] The heater 6 is a heating device for heating the aluminadischarge tube 2 to a desired temperature and is provided with a heatingwire 60 as a heating member, a power source 61 for supplying voltage tothe heating wire 60, and a voltage regulator 62 for controlling thevoltage supplied from the power source 61 to the heating wire 60 andconstituting a voltage controller together with the power source 61.

[0054] The heating wire 60 is a nichrome wire and, as shown in FIG. 2,is wound around the outer circumference of the alumina discharge tube 2so as to surround a predetermined location of the alumina discharge tube2. Specifically, the heating wire 60 is wound around a location below adischarge location where the waveguide 11 and the alumina discharge tube2 intersect. Further, the two ends of the heating wire 60 areelectrically connected to the voltage regulator 62 outside the chamber9. The voltage regulator 62 is electrically connected to the powersource 61.

[0055] Due to this, by turning the power source 61 on and adjusting thevoltage regulator 62 so as to control the voltage supplied to theheating wire 60, the heating wire 60 will rise to a temperaturecorresponding to the supplied voltage and the alumina discharge tube 2will be heated to the desired temperature.

[0056] Note that in FIG. 1, reference numeral 7 is an etching regionlimiter which is provided with a nozzle 70 attached to the chamber 9 ina state with its opening facing the inside of the chamber 9 and an N₂(nitrogen) gas storage cylinder 73 connected to this nozzle 70 through avalve 71 and a flow rate controller 72.

[0057] Next, an explanation will be given of the operation of the localetching apparatus of this embodiment. Note that since it is possible toexecute the local etching method according to the aspect of the presentinvention by operating the local etching apparatus, the explanation willbe given along with the steps of that method.

[0058] First, the plasma generation step is executed.

[0059] That is, by turning the power source 61 of the heater 6 shown inFIG. 1 on and controlling the voltage supplied to the heater wire 60 bythe voltage regulator 62, the heating wire 60 wound around the aluminadischarge tube 2 is heated and the temperature of the alumina dischargetube 2 is made to rise to a predetermined temperature T₀ by that heat.The temperature T₀ is the temperature shown in FIG. 11. With an aluminadischarge tube 2, it is for example 100° C. If the alumina dischargetube 2 is raised to over this temperature T₀, the etching depth of thewafer W in the later explained local etching step becomes substantiallyconstant.

[0060] When the surface temperature of the alumina discharge tube 2reaches the above mentioned T₀° C. by the execution of this heatingstep, the power source 61 is turned off and the plasma generation stepis executed.

[0061] That is, the vacuum pump 91 is driven to make the inside of thechamber 9 a predetermined low atmospheric pressure state and the Z-drive5 is operated to raise the X-Y drive 4 as a whole and bring the siliconwafer W close to the opening 21 of the nozzle portion 20.

[0062] Further, the valve 32 of the gas feeder 3 is opened to feed theSF₆ gas in the gas cylinder 31 through the feed pipe 30 to the inside ofthe alumina discharge tube 2. At this time, the opening degree of thevalve 32 and the flow rate controller 33 are adjusted to adjust the flowrate of the SF₆ gas to for example 300 sccm.

[0063] In parallel with the above operation of feeding the SF₆ gas, themicrowave generator 10 is driven. The microwave M causes plasmadischarge of the SF₆ gas and production of radicals G including F(fluorine) radicals. Due to this, the radicals G are guided into thenozzle portion 20 of the alumina discharge tube 2 and sprayed from thespray port 21 of the nozzle portion 20 to the silicon wafer W side.Suitably thereafter, the opening degree of the valve 71 of the etchingregion limiter 7 and the flow rate controller 72 are adjusted to adjustthe flow rate of the N₂ gas from the nozzle portion 20 to for example500 sccm, the pressure of the SF₆ gas inside the nozzle portion 20 ismade 1.5 Torr, and diameter of the flow of the radicals G sprayed fromthe nozzle portion 20 is reduced to limit the etching region to thedesired size.

[0064] The local etching step is executed in this state.

[0065] That is, the control computer 45 is used to drive the X-Y drive 4and make the chuck 90 holding the silicon wafer W move zigzag in the X-Ydirection.

[0066] Specifically, as shown in FIG. 3, the nozzle portion 20 is madeto scan the silicon wafer W relatively in a zigzag pattern. At thistime, the relative speed of the nozzle portion 20 with respect to thesilicon wafer W is set so as to be substantially inversely proportionalto the thickness of the relatively thick portion. Due to this, as shownin FIG. 4, the nozzle portion 20 moves directly over the non-relativelythick portion Wb at a high speed and falls in speed in accordance withthe thickness of the relatively thick portion Wa when coming above therelatively thick portion Wa. As a result, the etching time of therelatively thick portion Wa becomes longer and the relatively thickportion Wa is shaved flat. The entire surface of the silicon wafer W islocally etched in this way.

[0067] At this time, due to the heat of the plasma discharge, thetemperature of the alumina discharge tube 2 becomes higher than theabove mentioned temperature T₀, so the etching depth with respect to theentire surface of the silicon wafer W becomes substantially constant. Asa result, the surface of the silicon wafer W is flattened by asubstantially uniform etching depth.

[0068] After the processing for flattening one wafer W in this way isfinished, the microwave generator 10 of the plasma generator 1 shown inFIG. 1 is turned off to stop the plasma discharge and the power source61 of the heater 6 is turned on to execute the heating step. Due tothis, it is possible to maintain the lowest value of the fallingtemperature of the alumina discharge tube 2 after the plasma dischargeis stopped at the above temperature T₀.

[0069] In this state, a robot etc. is used and the gate valve 96 isopened to take out the silicon wafer W on the chuck 90, convey theprocessed silicon wafer W to a predetermined location, and set thesecond silicon wafer W on the chuck 90.

[0070] Suitably thereafter, when the plasma generation step is executed,the temperature of the alumina discharge tube 2 rises from a temperatureof an initial value of the temperature T₀. Therefore, it is possible toperform the local etching step on the second silicon wafer W immediatelywithout waiting for the temperature of the alumina discharge tube 2 torise to the temperature T₀. Similarly, it is possible to perform thelocal etching step on a third and later silicon wafers W immediately.

[0071] In this way, according to the local etching apparatus of thisembodiment, since it is possible to execute the local etching stepimmediately without waiting for the temperature of the alumina dischargetube 2 to rise to the temperature T₀ due to the preheating effect of theheater 6, it is possible to greatly increase the number of siliconwafers W processed per unit time, that is, the throughput.

[0072] The present inventors conducted the following experiments toprovide evidence of this point.

[0073]FIG. 5 is a graph of the correspondence between the time in thecase of performing the flattening work without preheating the aluminadischarge tube 2 and the temperature of the alumina discharge tube 2.FIG. 6 is a graph of the correspondence between the time in the case ofperforming the flattening work with preheating of the alumina dischargetube 2 and the temperature of the alumina discharge tube 2.

[0074] As shown in FIG. 5, during the work for flattening the firstsilicon wafer W, it takes 15 minutes for the temperature of the aluminadischarge tube 2 to reach the temperature T₀ when executing the plasmageneration step to cause plasma discharge at minute 0. Further, the5-minute local etching step was performed by minute 20, then the plasmadischarge was stopped and the transfer step executed. It tookapproximately 2 minutes for the transfer of the silicon wafer W.

[0075] Suitably thereafter, the work for flattening the second siliconwafer W was started at minute 22. At the time of this work, residualheat due to the plasma discharge at the work for flattening the firstsilicon wafer W remained. It therefore took 10 minutes for thetemperature of the alumina discharge tube 2 to reach the temperature T₀.Further, the 5-minute local etching step was executed by minute 37, thenthe plasma discharge was stopped and the 2-minute transfer step wasexecuted by minute 39.

[0076] Further, in the work for flattening the third and later siliconwafers W, the same time as the work for flattening the second siliconwafer W was required.

[0077] That is, as shown in FIG. 5, the flattening work for five siliconwafers W can be completed in 85 minutes.

[0078] As opposed to this, when preheating the alumina discharge tube 2before the flattening work, as shown in FIG. 6, since the aluminadischarge tube 2 was preheated, during the work for flattening the firstsilicon wafer W, the temperature of the alumina discharge tube 2 reachedthe temperature T₀ when executing the plasma generation step at minute0. It was therefore possible to execute the 5-minute local etching stepby minute 5. Further, when the plasma discharge was stopped and theheating step executed and the step for transferring the second siliconwafer W was performed in 2 minutes before minute 7, the temperature ofthe alumina discharge tube 2 was held at the temperature T₀ by theeffect of the heating step. The 5-minute local etching step for thesecond silicon wafer W could therefore be immediately performed byminute 12. Further, in the work for flattening the third and latersilicon wafers W, the same time as the work for flattening the secondsilicon wafer W was required.

[0079] That is, according to the local etching apparatus of thisembodiment, as shown in FIG. 6, the time by which it was possible tocomplete the flattening work for five silicon wafers W was just 33minutes. The throughput reached as much as about 2.6 times that of thecase of no preheating.

[0080] (Second Embodiment)

[0081]FIG. 7 is a sectional view of the essential portions of a localetching apparatus according to a second embodiment of the presentinvention. Note that parts the same as those shown in FIG. 1 to FIG. 6are explained given the same reference numerals.

[0082] This embodiment differs from the first embodiment in the pointthat use is made of an optical heater which heats the alumina dischargetube 2 by emitting infrared rays to the alumina discharge tube 2.

[0083] The optical heater 80, as shown in FIG. 7, is provided with aknown halogen heater 81 and a power source 82. At the time of operation,it is possible to specifically work the local etching method accordingto the aspect of the invention.

[0084] Specifically, the halogen heater 81 is arranged in a state withits front facing a location lower than the discharge location where thewaveguide 11 and alumina discharge tube 2 intersect. The infrared rays Sfrom the not shown lamp of this halogen heater 81 are directed towardthe above location of the alumina discharge tube 2 so as to heat thealumina discharge tube 2 to the above temperature T₀.

[0085] The rest of the configuration, mode of operation, andadvantageous effects are similar to those of the above first embodiment,so descriptions thereof will be omitted.

[0086] (Third Embodiment)

[0087]FIG. 8 is a sectional view of the essential portions of a localetching apparatus according to a third embodiment of the presentinvention. Note that parts the same as those shown in FIG. 1 to FIG. 6are explained given the same reference numerals.

[0088] This embodiment differs from the first and second embodiments inthe point that the heater is comprised of a thin tube wound around thealumina discharge tube 2 and fed with a fluid of a predeterminedtemperature so as to heat the alumina discharge tube 2.

[0089] The heater 83 is provided with a thin tube 84 as a heating block,a temperature control unit 85, and a fluid circulation pump 86. At thetime of operation, it is possible to specifically work the local etchingmethod according to the aspect of the invention.

[0090] The thin tube 84 is wound around the alumina discharge tube 2 ina state contacting its outside. The inside constitutes a fluid storageportion. The thin tube 84 passes through the inside of the temperaturecontrol unit 85 to reach the pump 86. The fluid feed port and fluidexhaust port of the thin tube 84 are connected to the exhaust side andintake side of the pump 86.

[0091] Due to this configuration, the fluid R inside the thin tube 84 ismade to circulate by the pump 86, is heated by the temperature controlunit 85, and heats the alumina discharge tube 2 to the above temperatureT₀.

[0092] The rest of the configuration, mode of operation, andadvantageous effects are similar to those of the above first and secondembodiments, so descriptions thereof will be omitted.

[0093] Note that the invention is not limited to the above embodiments.Various modifications and changes may be made within the scope of thegist of the invention.

[0094] In the first embodiment, the heater 6 was turned offsubstantially simultaneously with the execution of the plasma dischargestep and was turned on substantially simultaneously with the end of thelocal etching step, but it is also possible to leave the heater 6 on atall times to keep the temperature of the alumina discharge tube abovethe temperature T₀ at all times.

[0095] Further, in the first embodiment, a heating wire 60 was used asthe heating member, but it is also possible to use a heating plateinstead of the heating wire 60 and make the heating plate abut againstthe outside of the alumina discharge tube 2.

[0096] In the second embodiment, infrared rays S were used to heat thealumina discharge tube 2, but it is also possible to use a laser beametc. to heat it.

[0097] In the third embodiment, a thin tube 84 was used as the heatingblock, but as shown in FIG. 9 it is also possible to bring a hollow body87 having a fluid storage portion 87 a inside it into contact with theoutside of the alumina discharge tube 2, connect the thin tube 84 to afluid feed port 87 b and fluid exhaust port 87 c of the hollow body 87,and communicate the thin tube 84 to the fluid storage portion 87 a.

[0098] In the above embodiments, an alumina discharge tube 2 was used asthe discharge tube, but any of an aluminum nitride discharge tube,sapphire discharge tube, and quartz discharge tube may be used insteadof the alumina discharge tube 2.

[0099] For example, in the above embodiments, SF₆ gas was used as theradical R producing gas, but CF₄ (carbon tetrafluoride) or NF₃ (nitrogentrifluoride) gas may also be used. Further, it is also possible to feednot a single SF₆ gas, but a mixed gas of SF₆ gas and O₂ gas or other gasto the alumina discharge tube 2.

[0100] As explained in detail above, according to the present invention,since the discharge tube is preheated to at least a temperature at whichthe etching depth of the object to be etched becomes substantiallyconstant, there is no need to wait with the local etching work until thedischarge tube rises to that temperature by the heat resulting from theplasma discharge as in the conventional local etching apparatus.Therefore, it is possible to perform the local etching work immediately.As a result, there is the superior effect that it is possible to improvethe throughput of the flattening of the object to be etched.

What is claimed is:
 1. A local etching apparatus comprising: a dischargetube with a spray port of a nozzle portion facing an object to be etchedin a chamber; a plasma generator for causing plasma discharge of apredetermined gas in said discharge tube so as to produce radicals forlocally etching a relatively thick portion present on a surface of theobject to be etched; and a heater for heating said discharge tube to apredetermined temperature.
 2. A local etching apparatus as set forth inclaim 1 , wherein said heater is provided with: a heating memberprovided so as to surround said discharge tube and capable of raisingthe temperature in accordance with voltage applied thereto; and avoltage controller for controlling the voltage applied to said heatingmember.
 3. A local etching apparatus as set forth in claim 2 , whereinsaid heating member of said heater is a heating wire wound around saiddischarge tube.
 4. A local etching apparatus as set forth in claim 1 ,wherein said heater is an optical heater which emits infrared rays or alaser beam to said discharge tube to heat said discharge tube.
 5. Alocal etching apparatus as set forth in claim 1 , wherein said heater isprovided with: a heating block arranged so as to surround said dischargetube in a state contacting the outer side of said discharge tube and hasa fluid feed port and fluid exhaust port communicating with a fluidstorage portion at the inside; and a fluid feeder for heating the fluidto a predetermined temperature and feeding it to the fluid storageportion of said heating block.
 6. A local etching apparatus as set forthin claim 5 , wherein said heating block of said heater is comprised of athin tube wound around said discharge tube.
 7. A local etching apparatusas set forth in any one of claims 1 to 6 , wherein said discharge tubeused is any one of an alumina discharge tube, an aluminum nitridedischarge tube, a sapphire discharge tube, and a quartz discharge tube.8. A local etching method comprising: a plasma generating step forcausing plasma discharge of a predetermined gas in a discharge tube soas to produce radicals and spraying the radicals from a nozzle portionof the discharge tube; a local etching step for locally etching arelatively thick portion present on the surface of the object to beetched by the radicals sprayed from the nozzle portion while making thenozzle portion of the discharge tube move relatively along the surfaceof the object to be etched; and a heating step for heating the dischargetube at least to a time of start of plasma discharge of said plasmagenerating step to at least a temperature at which the etching depth ofthe object to be etched at said local etching step becomes substantiallyconstant.
 9. A local etching method as set forth in claim 8 , whereinsaid heating step is comprised of heating the discharge tube to thetemperature at all times.
 10. A local etching method as set forth inclaim 8 , wherein said heating step is comprised of heating thedischarge tube to the temperature until the start of plasma discharge ofsaid plasma generating step.
 11. A local etching method as set forth inany one of claims 8 to 10 , wherein said heating step is comprised ofheating a location of the discharge tube between the plasma dischargelocation and the spray port of the discharge tube to the temperature.12. A local etching method as set forth in any one of claims 8 to 11 ,wherein said heating step is comprised of raising a temperature of aheating member surrounding the discharge tube by application of voltageso as to heat the discharge tube to the temperature.
 13. A local etchingmethod as set forth in any one of claims 8 to 11 , wherein said heatingstep is comprised of emitting infrared rays or a laser beam to thedischarge tube to heat the discharge tube to the temperature.
 14. Alocal etching method as set forth in any of claims 8 to 11 , whereinsaid heating step is comprised of feeding a heated fluid into a heatingblock arranged so as to surround the discharge tube in a statecontacting the outer side of the discharge tube so as to heat thedischarge tube to the temperature.